Field of Invention
The present invention relates to a field of ultrasound imaging, and more particularly to a contrast imaging method based on a wide beam and a method for extracting a perfusion time-intensity curve (TIC).
Description of Related Arts
The conventional B-mode ultrasonography images via acoustic focus of the scanning lines one by one, at the frame rate about 60 Hz. In the meantime, in order to clinically obtain the high resolved ultrasonic image and imaging depth, the relatively higher acoustic power is usually employed, which may not only impair the tissues but also enhance damages to the microbubbles, so as to decrease the contrast-to-tissue ratio (CTR) to certain extent. Moreover, the conventional scanning mode line-by-line causes multiple times of damages to the microbubbles, which forces to clinically further enhance the perfusion concentration of the contrast agent in order to maintain a relatively high CTR. It is a clinical founding that the over high acoustic power and the over high concentration of the contrast agent may potentially threat the health of the human body, which restricts the further application of the ultrasound contrast imaging in the clinical medicine. Meanwhile, for the B-mode contrast imaging in vivo at the low frame rate, the respiratory movement and the organ involuntary peristalsis would generate the false movement track. The false movement track results in the apparent distinctions between the former frame and the latter frame, and thus affects the imaging quality, the accurate extracting of the subsequent TIC and the reliable evaluation of perfusion. Besides, the low frame rate has a poor performance in catching the rapidly-moving organ, resulting in the absence of the corresponding evaluation and the insensitivity to the instantaneous movement information. Accordingly, the rapid high-frame-rate contrast imaging emerged.
Conventionally, the widely applied ultrasound contrast imaging technologies basically employ the linearity or the non-linearity of the microbubble oscillation, such as the harmonic imaging, the harmonic power Doppler imaging, the pulse inversion imaging and the pulse inversion harmonic imaging. The high-frame-rate plane wave imaging enables the observation to the instantaneous change of the microbubbles and the monitoring to the rapid movement of the perfusion area, and contributes to the innovation in contrast mechanisms.
Therein, the pulse inversion (PI) is the common manner for obtaining the relatively high signal-to-noise ratio (SNR) through the apparent echo differences caused by the non-linearity of the microbubbles and the linearity of the tissues. The microbubble wavelet transform, based on taking advantage of the microbubble echo information as much as possible, suppresses the impact brought by the non-linear acoustic feature of the tissues to further increase the CTR and the detection sensitivity of the contrast microbubbles. The decorrelation is the manner for improving the CTR, by setting the decorrelation threshold based on the decorrelation difference of the contrast microbubbles and the surrounding tissues between the neighboring echo signals of the video frequency (VF) signals. The decorrelation not only has a relatively high sensitivity to the movement of the tissues, but also remedies the limitation of the PI and the microbubbles wavelet transform on the radio frequency (RF) signals by processing the VF signals.
The scattered echo signals obtained from the contrast imaging contain a series of physiological information. During the specific operations, the TIC is usually extracted to obtain time distribution information, such as the blood flow velocity, the blood volume and the hemodynamics. The echo signal enhancement induced by the microbubbles is proportional to the concentration, and thus is also proportional to the blood volume of the tissues, which converts the time distribution information denominated by the TIC into the spatial distribution information and promotes the development of the perfusion parametric estimation. Thus, a precise and rapid extracting of the TIC tendency plays an important role in the image quality of the parametric imaging and the authenticity of the evaluation and diagnosis of the blood perfusion.
There are various conventional processing methods after the extracting of the TIC, such as the baseline zeroing, the interpolation processing, the filtering processing and the function fitting or the perfusion model fitting. The wide beam contrast imaging is different from the conventional narrow beam contrast imaging, so as to greatly restrict the application of the conventional TIC processing methods, especially the application of the TIC perfusion model fitting. Accordingly, the present invention adopts a Detrended Fluctuation Analysis (DFA) fitting method, which not only divides TIC data into sections with consideration of an induced weight on an overlapped section by the data before and after a fitting section, and executes an auto adaptive non-linear polynomial fitting. Nevertheless, despite of being able to completely extract the TIC overall tendency, the conventional TIC processing methods, mostly based on the integral data fitting and the point-by-point processing, are still unable to accurately fit upon the partial dynamic tendency; moreover, due to the few original TIC data at the low frame rate, the single point exerts a relatively big weight upon the final fitting result. It is difficult for the subsequent processing to completely eliminate the impact on the overall TIC tendency brought by the partial singular points. In order to ensure the accuracy of the TIC fitting, it is also difficult to lower the time cost of the point-by-point processing.